The goal of the proposed project is to utilize a tumor model system, multicell spheroids in vitro, to collect quantitative information regarding the most effective methods of combining radiation and chemotherapy for tumor therapy. Our studies will be designed to elucidate any interaction between these modalities when concurrently or sequentially administered. We also intend to evaluate whether flow microfluorimetry monitoring of alterations of cell cycle kinetics induced by a treatment can be exploited to suggest optimum timing for subsequent treatment. The viability of each of the cycling, non-cycling, and hypoxic cell populations of the spheroids will be assayed during and after single and multiple treatments with the single or combined modalities. Individual cell populations will be selected for viability assay utilizing a Becton-Dickinson FACS-II cell sorter, and/or unit-gravity sedimentation with the Sta-put apparatus. Combinations of radiation and chemotherapeutic agents having an increased differential effect on the hypoxic/non-cycling populations will presumably lead to an improved therapeutic ratio in vivo, and multifraction application may further augment differential effects. In addition to cell viability studies using colony formation as the experimental endpoint, other indicators of spheroid response will be followed, including regression and regrowth rates, cell cycle kinetics, cellularity, and repair and repopulation of the spheroid in situ. We anticipate that these results will be directly applicable to both the planning and the rationalization of cancer treatment in man.